add bpf_passthrough generation

pythonbpf/vmlinux_parser/import_detector.py

@@ -2,6 +2,7 @@ import ast
 import logging
 import importlib
 import inspect
+import llvmlite.ir as ir
 
 from .assignment_info import AssignmentInfo, AssignmentType
 from .dependency_handler import DependencyHandler
@@ -76,9 +77,28 @@ def detect_import_statement(tree: ast.AST) -> list[tuple[str, ast.ImportFrom]]:
     return vmlinux_imports
 
 
+def bpf_passthrough_gen(module):
+    i32_ty = ir.IntType(32)
+    ptr_ty = ir.PointerType(ir.IntType(8))
+    fnty = ir.FunctionType(ptr_ty, [i32_ty, ptr_ty])
+
+    # Declare the intrinsic
+    passthrough = ir.Function(module, fnty, "llvm.bpf.passthrough.p0.p0")
+
+    # Set function attributes
+    # TODO: the ones commented are supposed to be there but cannot be added due to llvmlite limitations at the moment
+    # passthrough.attributes.add("nofree")
+    # passthrough.attributes.add("nosync")
+    passthrough.attributes.add("nounwind")
+    # passthrough.attributes.add("memory(none)")
+
+    return passthrough
+
+
 def vmlinux_proc(tree: ast.AST, module):
     import_statements = detect_import_statement(tree)
 
+    bpf_passthrough_gen(module)
     # initialise dependency handler
     handler = DependencyHandler()
     # initialise assignment dictionary of name to type